Pituitary neoplasms are associated with a great deal off morbidity of excessive hormone production and/or as space occupying lesions in the central nervous system. The mechanisms regulating pituitary tumor growth in humans are poorly understood. Recent studies have shown that pituitary adenomas are monoclonal and that some specific genetic alterations are present in these tumors. However, very little is known about the regulation of the pituitary tumor growth and why only few of these neoplasms become malignant, which usually leads to the patient's demise in spite of aggressive treatment. Our laboratory has recently developed human pituitary cell lines immortalized with a replication-defective recombinant human adenovirus which should provide stable cell lined for many of the proposed studies. We plan to examine the mechanisms regulating pituitary growth and tumor progression using cell and molecular biological approaches. Preliminary studies indicate that pancreastain, a proteolytic product of chromogranin, which is processed by PC 1/3 and PC 2 in pituitary cells, has autocrine and paracrine regulatory functions on pituitary tumor cells. Our preliminary studies also showed that pancreastain inhabits cell proliferation in vitro. The haploid insufficiency paradigm will be explored to possibly explain some of the effects of p27 on pituitary tumor development and progression. Our laboratory was the first to discover leptin production and secretion by anterior pituitary cells. We also noted that leptin inhabit plan to examine the mechanism of leptin action in the pituitary. The specific aims include: I. Determine the role of chromogranin/secretogranin proteolytic products and neuroendocrine-specific proconvertases in pituitary tumor growth and differentiation. II. Determine the role of specific cell cycle inhibitors in the development of pituitary tumors. a. Examine the mechanism regulating p27 expression in pituitary tumor development and progression. b. Determine the role of p16 methylation in pituitary tumor development. III. Examine the role of leptin, leptin receptors, STAT and SOCS proteins in pituitary tumor development and progression. The information derived from these studies should provide insight into the pathobiology of pituitary tumors and lead to more effective treatment modalities.